Development of Energy-Based Brittleness Index for Sandstone Subjected to Freeze-Thaw Cycles and Impact Loads

As one of the most important parameters of rock materials, brittleness is affected by external conditions such as temperature and dynamic disturbances. However, there is no universal criterion for brittleness. In this paper, the brittleness of sandstone subjected to rapid freeze-thaw (F-T) cycles and impact loads are investigated. The 25 specimens were subjected to different F-T cycles and impact loads and then investigated. It was found that the dynamic strength and Young's modulus of the specimens decrease, whereas porosity increases after the application of F-T cycles. The dynamic stress-strain curves demonstrated that after the peak point, the rock sample first exhibited class I behavior and then class II behavior. Previous studies implied that the brittleness index based on the pre-peak stress-strain characteristics was not sufficient to describe the rock fracture. Two brittleness indices based on the pre-peak and post-peak strain energy were thus derived using the complete dynamic stress-strain characteristics of rock samples. The two brittleness indices were strongly correlated with the physical parameters, such as porosity and mechanical parameters, including peak stress and dynamic modulus.